Flexographic printing is a rotary letter press printing process which traditionally uses flexible rubber, or other elastomer, printing plates and liquid, fast drying ink. An advantage of flexographic printing is its simple ink distribution system.
In flexographic printing, a web to be imprinted is passed between an impression cylinder and a plate cylinder, from which the ink is transferred to the web. Ink is applied to the plate cylinder in precisely-controlled quantities by an anilox metering roll. The circumferential surface of the anilox roll is divided into a very large number of small cells (typically, 15,000 cell per square centimeter). The surface of the anilox roll is flooded with ink, thus filling the cells on the roll's surface. Ink is fed to the anilox roll by an ink fountain. A commonly-used ink fountain comprises an ink reservoir and a pair of doctor blades which contact the anilox roll above and below the reservoir. The surface of the anilox roll, the doctor blades and the reservoir define a closed chamber for containing the ink. As the anilox roll rotates, the doctor blades shave surplus ink from the surface of the anilox roll so that ink is carried only in the interior of the cells on the roll's surface and not on the lands between cells. This results in a uniformly metered film of ink being applied to the surface of the plate cylinder.
Typically, the ink fountain extends the entire length of the anilox roll and plate cylinder. In cases where it is desired to print more than one color on a web, which requires more than one color of ink, the chamber containing the ink in the ink fountain is divided into two or more subchambers or compartments by ink dams or dividers. These dividers are designed to maintain a fluid-tight seal between compartments in the ink fountain and to maintain a seal against the anilox roll.
Ink fountain dividers per se are known in the art, and are illustrated in, for example, U.S. Pat. Nos. 3,381,517, 4,559,871, 4,667,595, and 4,796,528.
U.S. Pat. No. 3,831,517 discloses an apparatus for resiliently urging a seal member against a roller in the context of a fountain divider for a printing press ink fountain. The seal member is urged against the roller by a flat flexible spring strap with an arcuate outside surface which engages the sealing member. The biasing force exerted by the spring strap on the seal member can be adjusted by means of an adjusting rod, one end of which engages the spring strap and the other end of which engages a desired serration in a saw-toothed member.
U.S. Pat. No. 4,559,871 discloses divider plates for an ink dividing assembly for an inking roller in an ink fountain of a rotary printing press, with the divider plates resiliently biased against the ink roller. The divider plates are shown in conjunction with a chambered doctor blade assembly. The divider plates are slidingly mounted in guide plates. The front surface of the divider plates is curved and engages an inking roller. The divider plates are spring-biased into contact with the inking roller by leaf springs.
U.S. Pat. No. 4,667,595 discloses divider plates between axially-spaced doctor bars in an inking system for a rotary printing press. The divider plates rotate about a pin whose axis is parallel to the axis of the inking roller so that they are biased against the inking roller by gravity.
U.S. Pat. No. 4,796,528 shows a separator element located within a chambered doctor blade ink fountain to separate the fountain into axial zones. The separator element comprises a separator strip which extends over a portion of the surface of an anilox roller. A thin film of liquid, such as water or an aqueous solution of alcohol, is supplied to the separator strip so that the strip rides on a liquid film between the strip and the anilox roller, thus forming a fluid seal between axial zones in the ink fountain.
It will be appreciated that all of these prior arrangements are mechanically very complex. They are thus expensive to fabricate, require careful and precise alignment, and are susceptible to misalignment in use. There is therefore a need for a simple, inexpensive divider seal which is easy to fabricate and install, requires no time-consuming alignment, can compensate for wear and misalignment, and still provides an effective divider seal. The present invention fulfills that need.